Rebaudioside A is a high-potency diterpenoid glycoside sweetener having the chemical structure:
Rebaudioside A is isolated and extracted, along with other steviol glycosides, from the Stevia rebandiana (Bertoni) plant (“Stevia”), which is commercially cultivated in Japan, Singapore, Taiwan, Malaysia, South Korea, China, Israel, India, Brazil, Australia, and Paraguay. It is an alternative non-caloric sweetener with functional and sensory properties superior to those of many high-potency sweeteners. Processed forms of Stevia can be 3 to 300 times more potent than sugar; however, Stevia also has a bitter component. Of the four major diterpenoid glycoside sweeteners present in Stevia, rebaudioside A has been identified as the least bitter, and with the least persistent aftertaste. Bitterness often is significantly due to the impurities in extracts.
Current Joint FAO/WHO Expert Committee on Food Additives (JECFA) standards require that the total amount of steviol glycosides be purified to 95% or greater. Compositions of steviol glycosides currently are only available having from 80-92 steviol glycosides by weight—with the cost of these compositions increasing substantially as the purity levels of the steviol glycosides and/or rebaudioside A are increased. In addition, these compositions generally fail to provide sufficient purities of rebaudioside A among the steviol glycosides (e.g., generally having only ≦80% rebaudioside A by weight).
Previously reported efforts to purify rebaudioside A from mixtures of rebaudioside A and stevioside require numerous repeated purification steps. U.S. Pat. No. 5,962,678 discloses the re-crystallization of rebaudioside A using an anhydrous methanol solution to obtain an 80% pure rebaudioside A. By repeating the re-crystallization with anhydrous methanol numerous times, the purity of rebaudioside A may be increased to over 95%. U.S. Patent Publication No. 2006/0083838 discloses purification of rebaudioside A through re-crystallization with a solvent comprising ethanol and between 4 and 15% water. Japanese Patent Application No. 55-23756 discloses a method for purifying rebaudioside A and stevioside by crystallization from aqueous ethanol (>70%) to obtain an 80% pure rebaudioside A. U.S. Patent Publication No. 2007/0082103 discloses a method for purifying rebaudioside A by recrystallization from aqueous ethanol, asserting a two-step recrystallization from crude rebaudioside (60%) results in the formation of >98% pure rebaudioside at 97% yield. These prior art methods, however, do not provide a substantially pure steviol glycoside composition nor a rebaudioside A compositions of sufficient purity using only a single recrystallization step which is capable of satisfying current JECFA standards.
Accordingly, there exists a need for a simple, efficient, and economical method for preparing substantially pure steviol glycoside and rebaudioside A compositions.